Girls, Why do girls mistake a guy's happiness and self-satisfaction for haughtiness and vanity?

I love who I've become and the life I've made a great deal. I've worked hard to succeed in college, both academically and on my physical well-being. I started college as a skinny, unconfident guy who was scared to even talk to most girls for fear of rejection. I've worked to get myself stronger and bigger and I now weigh just over 200 pounds, which is a huge accomplishment considering where I came from (135 lbs). I no longer feel like a little boy in comparison to other guys and I feel attractive to girls for the first time in my life. In addition, I'm starting a grad program this fall as one of only two entering students with almost total financial support from my department. Life is good, and I'm so happy with what I've accomplished.

What I don't get, though, is the reaction I get from girls. A lot of girls I meet seem to think that the pride I have in myself is a sign of vanity and narcissism. It's not at all, though. I went from not liking myself to really loving myself, and it wasn't easy, but that isn't the same as narcissism. Girls say all the time that they want confident guys, but when it comes down to it, girls can be hypersensitive to any signs of personal pride in a guy. It's like they want a guy who is confident, but not *too* confident. Why is this?